Generally speaking, there are a variety of helical piers available on the market. Helical piers have a slender shaft with a helically shaped plate attached to it. When the shaft is rotated, the plate spirals into the soil, thus pulling the pier deeper down. Helical piers are often used to pull shaft-like extensions into the soil. Extensions are usually elongated, relatively slender bars which are attached to the shaft of the helical pier or to another extension. Together, helical piers and extensions form an in-ground load-bearing anchor or structure. If the in-ground structure needs to be positioned deep into the soil, multiple extensions may be connected in succession, the first one being attached to the trailing end of the helical pier's shaft, and each subsequent extension being attached to the trailing end of the preceding extension. The in-ground structure has a very high load-bearing capacity. Once inserted into the soil, helical piers remain there permanently; i.e. they are not designed to be pulled out and reused. Conventional helical piers and extensions can be obtained, for example, as Square-Shaft Helical-Piers marketed by the A.B. Chance Company of Centralia, Mo.
When the rotation of the helical pier stops, it and the attached extension sections, if any, are firmly anchored in the soil. The trailing end of the last extension (or the trailing end of the helical pier's shaft, if no extensions were used) protrudes above-ground, thus providing a tying point for above-ground structures. Depending on the weight of the above-ground structure, several helical piers may be arranged over a suitable area in order to provide the needed support. A variety of the above-ground structures may be erected over helical piers and extensions. Some examples of the above-ground structures are telecommunication towers, retaining walls, buildings, bridges, walkways and boat moorings.
The benefits of helical piers which pull the extensions into the soil as the piers spin have been recognized for a long time. The helical piers available on the market usually have a cutting tip formed by a slanted surface that extends over the cross-section of the shaft and forms a slanted cutting edge at the penetrating end of the shaft. Such helical piers tend to work well in soft soils, i.e. the soils that lack significant rock content, either loose or compact. When used in rocky soils, i.e. the soils with significant rock content, the prior art helical piers penetrate less well. At least in part this is believed to be due to the fact that the cutting edge and the adjoining cutting surface are not well-suited for spiraling through the high rock content in the soil. A helical pier should penetrate soil at the rate of about one pitch of the helical plate per shaft revolution so that the helical plate of the pier can spiral into the soil as it is rotated without significantly disturbing the surrounding soil. At least in part due to the hardness of the rocky soil, the prior art helical piers are at times unable to penetrate by a full helical pitch per revolution. This results in soil displacements around the helical plate as it seeks to spiral into the soil during each revolution, which slows the vertical travel of the helical pier during each revolution to less than the pitch of the helical plate, disturbs the surrounding soil and reduces its load-bearing capacity.
This slowdown of the vertical progress of the helical pier into the soil as it is rotated is believed to be caused at least in part by the inefficient configuration of the cutting edge/surface of conventional helical piers. Since helical piers are not reusable, that is, once anchored in the ground they remain there permanently, the penetrating ends of conventional helical piers are simply defined by the tapered surface and the cutting edge it forms. Tapered ends of this type are helpful for impact driving elongated posts and the like into the ground. They are ill-suited to form a hole in the ground for the shaft of the helical pier, because while the helical pier rotates and is forced deeper into the soil, its penetrating end must open the hole into which the shaft of the pier can extend. Elongated shafts with tapered ends can loosen the soil as they advance into it, but they have no way of effectively removing soil as it is being loosened from the vicinity of the penetrating tip. As a result, the forward progress of the rotating helical pier may be less than the pitch of the helical pier per revolution. When that occurs, the helical plate of the pier will disturb the surrounding soil, loosen its compactness, and compromise the stability with which the helical pier is left in the ground.
This situation could be remedied by forming the elongated shaft of helical piers with elongated, debris-removing flutes, as are common in conventional drills. However, this is not practical for use with helical piers for at least two reasons. First, providing the elongated shaft of the pier with flutes that extend over the length of the shaft would greatly weaken the shaft. Here, strength is one of its primary requirements because, once placed in the soil, the shaft must carry the above-ground structure that will be secured to it.
In addition, providing the helical pier shaft with flutes over its length would greatly increase its cost. Shafts for helical piers are relatively heavy, solid steel bars which exhibit the desired strength and are relatively inexpensive to produce. A simple tapered end for the shaft, as used on prior art helical piers, can be very inexpensively formed, for example, by sawing, milling, forging, molding and other well-known shaping processes. The cost of the shaft of a helical pier would multiply if it had to be separately machined to provide debris-removing flutes or passages over the length of the shaft.
Other prior art piers depend on a repetitive application of an impact force to drive the rotating pier deeper into the soil. Such piers require special tools that provide both torque and impact. Furthermore, the tip of these impact tools must be made of very hard material, to prevent damage to the tool tip caused by repetitive impacts against rocks in the soil.
Yet some other piers are made of strong pipes with a drill bit at the leading edge. During the drilling, drilling fluids are pumped through the pipe. The flow of drilling fluid rotates the drill bit at the end of the pipe. The drilling fluid on its return path washes the removed soil along the outside surface of the pipe back to the surface. Therefore, a complete auguring of the soil around the rotating drill is done, which significantly weakens the carrying capacity of the in-ground structure.
Thus, there exists a need for a reasonably priced helical pier capable of penetrating even rocky soil without disturbing the compactness of the surrounding soil so that the helical pier becomes firmly anchored in the soil and provides a high load-bearing anchor capable of supporting relatively heavy loads.